Theoretical Diversity Improvement in Frequency-Shift Keying

Methods of using diversity to improve frequencyshift keyed receptions in the presence of Rayleigh fading are analyzed. In the absence of prior information about signal amplitude and phase, square-law combination is optimum; the error rate for this combination method has been found. If signal amplitude and phase are exactly known prior to reception of the signal, coherent combination and detection are optimum; at low error probability this yields only a 3-db improvement. Nonoptimum switch diversity yields only slightly less diversity gain than square-law combination. For dual diversity, correlation of the fading on the separate antennas does not give a large loss if the correlation coefficient is moderate. Correlated noise yields a similar small loss.